Interaction of Tamarisk Legacy Soil and Climate Change on Fremont Cottonwood
Julia Hull1, Kevin Hultine2, Lisa Markovich3, Catherine Gehring4
1Northern Arizona University, Flagstaff, AZ, USA; jbh232@nau.edu
2 Desert Botanical Garden, Phoenix, Arizona, USA; khultine@dbg.org
3 Northern Arizona University, Flagstaff, Arizona, USA; Lisa_Markovchick@nau.edu
4 Northern Arizona University, Flagstaff, Arizona, USA; Catherine.Gehring@nau.edu
The conservation and restoration of riparian ecosystems in the southwestern U.S. is becoming increasingly important under climate change, altered hydrologic regimes, and the spread of non-native species. Restoration of native species, such as Fremont cottonwood (Populus fremontii), to Tamarix spp. (tamarisk, saltcedar) invaded lands may face complications imposed by tamarisk legacy soil. Tamarisk can alter soil chemical and biological properties, which can last for years following mortality or removal. This is further complicated by the disproportionate effect climate change is having on the desert southwest. Understanding the interaction of tamarisk legacy soil and increased temperature due to climate change will be important for the implementation of effective restoration practices in the southwest in the coming decades. To that end, we used a fully-factorial greenhouse experimental design to test the hypothesis that the combined effects of higher temperatures and tamarisk legacy soil would have synergistic negative effects on the performance of cottonwoods. We collected cottonwood cuttings from four populations, which were grown in ambient or heated temperature conditions (~3.5 C warmer than ambient) either in tamarisk legacy or agriculture legacy soil. Our treatment soils were collected from adjacent plots in an experimental garden in Yuma, Arizona. We measured cottonwood mortality, growth, biomass allocation patterns, and functional traits. We found 1) a synergistic interaction of temperature and soil legacy only in cottonwood mortality, and 2) functional traits associated with water supply and demand, as well as biomass allocation, showed buffering effects, meaning that surviving cottonwoods grown in heated-tamarisk soil treatment outperformed other treatment combinations. The implications of this study suggest that the combined effects of higher temperature and tamarisk legacy soil may not be as dire as previously predicted. Although mortality in the heated-tamarisk soil treatment was ~65%, the surviving individuals showed better acclimation to the combined stressors. Land managers interested in the restoration of tamarisk invaded lands while preparing for current and future climate change may consider increasing the number of plants in a restoration project to accommodate for high mortality with an understanding that the survivors may be better suited to face the combination of tamarisk legacy soil and high temperatures.